Doherty Amplifier with Adjustable Alpha Factor

ABSTRACT

A Doherty amplifier circuit having a tunable impedance and phase (“TIP”) circuit to provide an adjustable alpha factor, which allows for a selection of power added efficiency (PAE) curves that are useful for applications having different modulations or to meet other criteria. Embodiments include a Doherty amplifier having a TIP circuit that provides for tunability of the impedance Z INV  (resulting in an adjustable alpha factor) while maintaining the phase of the output of the carrier amplifier at 90° (for a selected polarity)±a low phase variation. Embodiments of the TIP circuit include one or more series-connected TIP cells comprising at least one TIP circuit combined with a tunable phase adjustment circuit. In operation, when the impedance of a TIP cell is adjusted, adjustments within the cell are also made to provide a phase shift correction back towards 90° (at the selected polarity).

BACKGROUND (1) Technical Field

This invention relates to electronic circuits, and more particularly toradio frequency amplifier circuits.

(2) Background

Many modern electronic systems include radio frequency (RF)transceivers; examples include personal computers, tablet computers,wireless network components, televisions, cable system “set top” boxes,radar systems, and cellular telephones. Many RF transceivers are quitecomplex two-way radios that transmit and receive RF signals acrossmultiple frequencies in multiple bands using one or more signalingprotocols. As an example, a modern “smart telephone” may include RFtransceiver circuitry capable of operating on different cellularcommunications systems (e.g., GSM and CDMA), on different wirelessnetwork frequencies and protocols (e.g., IEEE 802.1bg at 2.4 GHz, andIEEE 802.1n at 2.4 GHz and 5 GHz), and on “personal” area networks(e.g., Bluetooth based systems).

In portable battery-operated devices, such as cellular telephones, RFpower amplifiers (PAs) in RF transceivers consume a significant part ofthe total device current, thus impacting battery life. Accordingly,reducing the average PA current will extend battery life and prolong“talk time”, defined as the time it takes to discharge the devicebattery while on a telephone call or transmitting or receiving data.

Cellular phone systems require a handset PA to output a range of powerlevels, depending on distance to a base station and signal pathconditions. The efficiency of such systems can be expressed by apercentage: power added efficiency (PAE), defined as (RF power out−RFpower in)÷DC power supplied; higher percentages are desirable. Effortshave been made to maximize PAE at full power level, and in some systems(e.g., GSM cellular systems), PAE has reached 50-60% at full power. Ithas been suggested that improving PAE at lower power levels would bebeneficial as well, thus increasing average PAE across power levels;see, for example, Darren W. Ferwalt, “A Base Control Doherty PowerAmplifier Design for Improved Efficiency in GSM Handsets”, § 1.1 and §1.2, Masters of Science Thesis at Oregon State University, Dec. 10,2003.

One method to achieve improved PAE at lower power levels was originallydeveloped by William Doherty, as described in U.S. Pat. No. 2,210,028,issued Aug. 6, 1940. FIG. 1A is a simplified schematic diagram of aprior art Doherty amplifier 100. A Doherty amplifier 100 is composed ofa carrier amplifier 102 coupled in parallel with a peaking amplifier104; the amplifiers 102, 104 may be, for example, MOSFET-based circuits.An RF input signal, RF_(IN), is applied directly to the carrieramplifier 102 with no phase shift, and indirectly to the peakingamplifier 104 through a quarter wave transmission line L1 that shiftsthe phase of RF_(IN) by −90°. The output of the carrier amplifier 102 isphase shifted by −90° by a quarter wave transmission line L2 andcombined in phase with the output of the peaking amplifier 104 toprovide an amplified RF output signal, R_(OUT), at a load resistance,R_(L). The quarter wave transmission line L2 is also known as animpedance inverter and has a characteristic impedance (Z₀) of Z_(INV).

In operation, both amplifiers 102, 104 are ON at full power, while atlow power levels the peaking amplifier 104 is OFF. The two amplifiers102, 104 are configured such that as the power out of the peakingamplifier 104 is reduced, the load impedance of the carrier amplifier102 is increased, allowing the carrier amplifier 102 to operate athigher efficiency at a lower power levels. The combined efficiency atreduced power is therefore improved over that of a single amplifier.

A problem of conventional Doherty amplifiers 100 is that, while theiroutput may be applied to a tunable impedance matching network to provideimpedance matching for different RF bands, they have a constant alphafactor, α=R₁/Z_(INV). For example, FIG. 1B is a graph 150 of amplifierefficiency as a function of output power, Pout, for a prior art Dohertyamplifier having a constant alpha factor of 0.25 (graph curve 152), andfor a prior art Doherty amplifier having a constant alpha factor of 0.5(graph curve 154); a dashed graph curve 156 shows the characteristicsfor an ideal class B amplifier. For some applications, an alpha factorof 0.25 may be preferred, while for other applications, an alpha factorof 0.5 may be preferred (of course, other alpha factors can be used).

A constant α is not beneficial across different modulation schemes, suchas the modulation schemes used in cellular telephone systems (e.g., LongTerm Evolution (LTE), 5G NR, WDCMA, CDMA, GSM, etc.), WiFi LANS, andother wireless transmission systems, particularly those usingbattery-powered transceivers. These modulation schemes have differentpeak to average ratios of power. The amplifier must be able to handlethe peak power but is more frequently operated at the lower averagepower. These peak to average ratios currently range from 0 dB to about 7dB. A single fixed Doherty amplifier employed for all these modulationschemes will suffer from poorer PAE at the high peak to average ratios.

Accordingly, there is a need for a Doherty amplifier circuit having anadjustable alpha factor. The present invention meets this need.

SUMMARY

Embodiments of the present invention encompass a Doherty amplifiercircuit having a tunable impedance and phase circuit to provide anadjustable alpha factor. The adjustable alpha factor allows for aselection of power added efficiency (PAE) curves that are useful forapplications having different modulation schemes or to meet othercriteria. In particular, an adjustable alpha factor allows the secondaryPAE peak to be adjusted so that the overall PAE can be optimized fordifferent modulations (peak-to-average ratio) and also for average powerlevel. Embodiments maintain good PAE over a wide range of power levels.

Embodiments include a Doherty amplifier in which the conventionaldistributed quarter wave transmission line impedance inverter isreplaced by a tunable impedance and phase (“TIP”) circuit. Thecharacteristics of the TIP circuit are that it provides for tunabilityof the impedance Z_(INV) (thus resulting in an adjustableα=R_(L)/Z_(INV)) while maintaining the phase of the output of thecarrier amplifier at 90° (for a selected polarity)±an acceptably lowphase variation.

Various embodiments of the TIP circuit include one or moreseries-connected tunable and phase impedance cells comprising at leastone tunable impedance circuit combined with at least one tunable phaseadjustment circuit. In operation, when the impedance of a tunableimpedance and phase cell is adjusted, adjustments within the cell arealso made to provide a phase shift correction back towards 90° (at theselected polarity).

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1A is a simplified schematic diagram of a prior art Dohertyamplifier.

FIG. 1B is a graph of amplifier efficiency as a function of outputpower, Pout, for a prior art Doherty amplifier having a constant alphafactor of 0.25, and for a prior art Doherty amplifier having a constantalpha factor of 0.5; a dashed graph curve shows the characteristics foran ideal class B amplifier.

FIG. 2 is a simplified schematic diagram of a Doherty amplifier thatprovides an adjustable alpha factor with low phase shift.

FIG. 3A is a schematic diagram of a first embodiment of a tunableimpedance and phase circuit.

FIG. 3B is a schematic diagram of a second embodiment of a tunableimpedance and phase circuit.

FIG. 4 is a schematic diagram of a third embodiment of a tunableimpedance and phase circuit.

FIG. 5A is a schematic diagram of the Doherty amplifier of FIG. 2 inwhich the block symbol representing the tunable impedance and phasecircuit has been replaced by one tunable impedance and phase cell of thetype shown in FIG. 3A.

FIG. 5B is a schematic diagram of a modified version of the Dohertyamplifier of FIG. 2 in which the block symbol representing the tunableimpedance and phase circuit has been replaced by one tunable impedanceand phase cell of the type shown in FIG. 4.

FIG. 6 is a graph showing PAE as a function of power input (Pin) fordifferent values of Z_(INV) for a modeled tunable impedance and phasecell of the type shown in FIG. 3A, using the values shown in TABLE 1.

FIG. 7 is a process flow chart showing a first method of making aDoherty amplifier.

FIG. 8 is a process flow chart showing a second method of making aDoherty amplifier.

FIG. 9 is a process flow chart showing a third method of making aDoherty amplifier.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

Embodiments of the present invention encompass a Doherty amplifiercircuit having a tunable impedance and phase circuit to provide anadjustable alpha factor. The adjustable alpha factor allows for aselection of power added efficiency (PAE) curves that are useful forapplications having different modulation schemes or to meet othercriteria. In particular, an adjustable alpha factor allows the secondaryPAE peak to be adjusted so that the overall PAE can be optimized fordifferent modulations (peak-to-average ratio) and also for average powerlevel. Embodiments maintain good PAE over a wide range of power levels.

The transmission lines L1, L2 of a conventional Doherty amplifier can beapproximated with lumped element circuits, and in some applications, thelumped element circuits may be tunable. However, simply replacing theconventional impedance inverter L2 with a tunable lumped elementequivalent circuit, such as a tunable LC low pass filter, results in acircuit in which the alpha factor can be adjusted (by adjusting the L orC values to change Z_(INV)—and thus the characteristic impedance Z₀—forthe lumped element circuit), but in which the phase of the output of theinverter L3 shifts substantially away from an optimal 90° value (for aselected polarity), thus altering the impedance transformation for thecarrier amplifier 102, and also altering the phase alignment when theoutputs of the amplifiers 102, 104 are combined. This will cause a lossin power due to combining the two signals out of phase.

FIG. 2 is a simplified schematic diagram of a Doherty amplifier 200 thatprovides an adjustable alpha factor with low phase shift. The amplifiercircuit is similar to the circuit of FIG. 1A, except that theconventional distributed quarter wave transmission line impedanceinverter L2 is replaced by a tunable impedance and phase (“TIP”) circuit202. The characteristics of the TIP circuit 202 are that it provides fortunability of the impedance Z_(INV) (thus resulting in an adjustableα=R_(L)/Z_(INV)) while maintaining the phase of the output of thecarrier amplifier 102 at 90° (for a selected polarity, positive ornegative)±an acceptably low phase variation; for many applications, thelow phase variation would be about ±10°, but lower phase variationranges are achievable, as described below.

Various embodiments of the TIP circuit 202 include one or more stages oftunable circuits that provide a 90° phase shift (of a selected polarity)to the input signal and a tunable impedance. This may allow for tightercontrol of phase variation over frequency. For example, FIG. 3A is aschematic diagram of a first embodiment of a tunable impedance and phasecircuit 300 a. In the illustrated embodiment, an RF input signal (e.g.,from the carrier amplifier 102) RF_(IN) is coupled through one or moreseries-connected tunable impedance and phase (“TIP”) cells 302 toRF_(OUT). In this example, each TIP cell 302 includes a “pi” type CLCcircuit comprising a series inductor L1 and two bracketing tunable shuntcapacitors C1, which generally have the same range of values. Inaddition, a tunable capacitor C11 is coupled in parallel with the seriesinductor L1, thereby forming a tunable inductor circuit 304 (shownwithin the dotted oval).

More particularly, the TIP cell 302 in FIG. 3A may be viewed as a lumpedelement approximation of a transmission line. Multiple TIP cells 302 maybe cascaded to increase the bandwidth of the lumped element transmissionline; in general, each successive TIP cell 302 is a smaller step inphase. Making the lumped elements tunable allows tuning or adjustment ofthe characteristic impedance and the phase shift of the network. Whileeither or both of tunable inductors and tunable capacitors may be usedfor such lumped elements, tunable inductors tend to consume significantintegrated circuit area. However, a tunable inductor may be realized byplacing a tunable capacitor (e.g., C11) in parallel with a fixedinductor (e.g., L1), as in the example tunable inductor circuit 304 ofFIG. 3A.

In operation, the impedance and phase of a TIP cell 302 may be adjustedby changing the size and/or ratio of the tunable impedance and tunablecapacitance lumped elements. In the specific example of the TIP cell 302of FIG. 3A, tuning of both impedance and phase may be accomplished bytuning the capacitors C1 and C11. Accordingly, Z_(INV) may be adjustedfor a coupled carrier amplifier 102 as needed to achieve a selected afactor while making a phase shift correction back towards 90° (of theselected polarity) for proper amplifier function. Tuning of C1 and C11may be a concurrent or an iterative process since each of C1 and C11affect the impedance and the phase of the TIP cell 302. In practice, acalibration process may be performed that maps tuning states of C1 andC11 such that a desired impedance and phase shift can be achieved byconcurrently adjusting C1 and C11 to specific values, without using aniterative process. Alternatively, such mapping may be done by designand/or simulation. The mapped values may be stored in a lookup table.Such a lookup table may include functions such as inputting a desiredmode (e.g., a certain transmission configuration, such as for an LTEcell system), mapping that mode to desired component values for adesired a factor, and outputting the tuning values to adjust C1 and/orC11. Alternatively, the tuning states of C1 and C11 may be dynamicallyadjusted in a closed-loop manner by measuring the phase and impedance ofthe output of the TIP cell 302 and readjusting the tuning values of C1and/or C11 as needed to achieve a desired impedance and phase shift.

Stated another way, each example TIP cell 302 in FIG. 3A can be regardedas two coupled circuits, one primarily for adjusting impedance and theother primarily for adjusting phase, but is better regarded as a singletunable circuit that can concurrently tune impedance and phase.Regardless of characterization, embodiments of the invention enableadjustment of the alpha factor, thus allowing the secondary PAE peak tobe adjusted so that the overall PAE can be optimized for differentmodulations (peak-to-average ratio) and also for average power level.

FIG. 3B is a schematic diagram of a second embodiment of a tunableimpedance and phase circuit 300 b. The illustrated circuit isessentially the same as the circuit of FIG. 3A (some reference labelshave been omitted to avoid clutter), except that pairs of shuntcapacitors C1 in FIG. 3A situated between the inductors L1 of adjacentTIP cells 302 are replaced by a single “shared” capacitor C1′, thussaving components and integrated circuit die area. In general, the valueof capacitor C1′ should be about the sum of the pair of capacitances C1that are replaced by capacitor C1′ (thus, if the capacitors C1 of areplaced pair are of equal value, then capacitor C1′ generally should beabout twice the capacitance of a C1 capacitor).

FIG. 4 is a schematic diagram of a third embodiment of a tunableimpedance and phase circuit. In this example, a tunable impedance andphase (“TIP”) cell 400 comprises a “pi” type LCL circuit including aseries capacitor C1 and two bracketing shunt inductors L1. In addition,a pair of tunable capacitors C11, which generally have the same range ofvalues, are coupled in parallel with the shunt inductors L1, therebyforming a tunable inductor circuit 402 (shown within the dotted ovals).Note that the illustrated TIP cell 400 functions as a high-pass networkthat would provide a +90° base phase shift, and accordingly needs aninput that is shifted +90° to function properly (for example, see FIG.5B below).

The TIP cell 400 is thus the “LCL” dual of the “CLC” TIP cell 302 ofFIG. 3A, and is tunable in a similar manner. As described above, tuningof C1 and C11 may be a concurrent or an iterative process, since each ofC1 and C11 affect the impedance and the phase of the TIP cell 302.Similarly, calibration, mapping, and/or closed-loop adjustment processesmay be applied, as described above for the TIP cell 302 of FIG. 3A.

Note that the polarity of phase shift of particular subcircuits may bevaried in other embodiments. The key is that the phase shifts line up sothat the outputs of the carrier amplifier 102 and the peaking amplifier104 combine in phase. For example, some embodiments may use a −90° phaseshift in front of the carrier amplifier 102, or a −90° phase shift infront of the peaking amp (as described above with respect to FIG. 1A),so long as the outputs of the amplifiers 102, 104 are properly shiftedto combine in phase. Transmission lines may also be used to create thevarious phase shifts required.

For complete context, FIG. 5A is a schematic diagram 500 of the Dohertyamplifier of FIG. 2 in which the block symbol representing the tunableimpedance and phase circuit 202 has been replaced by one tunableimpedance and phase cell 302 of the type shown in FIG. 3A.

Similarly, FIG. 5B is a schematic diagram 520 of a modified version ofthe Doherty amplifier of FIG. 2 in which the block symbol representingthe tunable impedance and phase circuit 202 has been replaced by onetunable impedance and phase cell 400 of the type shown in FIG. 4. Inthis example, the input to the carrier amplifier 102 is shifted by −90°phase with respect to the direct input to the peaking amplifier 104,since the TIP cell 400 is a high-pass network.

As one of ordinary skill in the art would recognize, there are numerousother ways of implementing a tunable impedance and phase circuit thatprovides for tunability of the impedance Z_(INV) (thus resulting in anadjustable a) while maintaining the phase of the output of the carrieramplifier 102 at 90° (of a selected polarity)±an acceptably low phasevariation. For example, embodiments of the invention may be implementedusing tee-type (also known as “T-type”) tuning networks that are theduals of the “CLC” or “LCL” pi-type tuning networks of FIGS. 3A and 4,respectively. As additional examples, embodiments of the invention maybe implemented using other types of tuning networks, including (but notlimited to) LC, CL, low-pass, high-pass, etc., circuits in varioustopological configurations, such as pi, tee, bridged-T, L-pad, etc.

The tunable capacitors C1 and C11 need not have the same range ofvalues, and the range of values may vary among the TIP cells 302. One ormore of the tunable capacitors C1, C11 may comprise, for example, adigitally tunable capacitor (DTC) of the type described in U.S. Pat. No.9,024,700, issued on May 5, 2015, entitled “Method and Apparatus for usein Digitally Tuning a Capacitor in an Integrated Circuit Device” or inU.S. Pat. No. 9,197,194, issued on Nov. 24, 2015, entitled “Method andApparatus for Use in Tuning Reactance in a Circuit Device”, the contentsof both of which are hereby incorporated by reference. The inductor L1may be fixed (as shown in FIGS. 3A, 3B, and 4), or may be variable, suchas a digitally tunable inductor (DTL) of the type described in U.S. Pat.No. 9,197,194.

While it is beneficial to fabricate all of the components of a TIP cell302 on an integrated circuit (IC) die, some components may be off-die.For example, in the examples shown in FIGS. 3A, 3B, and 4, it may beuseful to use off-die inductors for L1 since IC inductors often consumesignificant die area.

Series connecting multiple TIP cells 302, as in FIG. 3A, betterapproximates the characteristics of a transmission line, increases thebandwidth of the circuit, and improves the tolerance of the phase shiftcapability (some modeled examples of the circuit of FIG. 3A can maintainthe phase of the output of the carrier amplifier 102 at 90°±˜5° orbetter for a selected polarity). However, in some embodiments, it may beuseful to connect multiple TIP cells 302 in parallel, or in aconfiguration with some TIP cells 302 connected in parallel and some TIPcells 302 connected in series (e.g., a parallel-series configuration ora mesh configuration).

SPECIFIC EXAMPLE

In one modeled example of a TIP cell 302 of the type shown in FIG. 3A,capacitors C1, C11 were implemented with DTCs, with the DTCs for the C1capacitors having the same range and settings; a fixed value (13.9 nH)inductor L1 was used for the model. By setting the DTC's to the valuesshown in TABLE 1 below, the characteristic impedance Z₀ (=Z_(INV)) ofthe TIP cell 302 can be varied over a range of about 70Ω to about 190Ωwhile maintaining a −90°±10° phase shift over a frequency range of825-925 MHz.

TABLE 1 C11 (pF) C1 (pF) L1 (nH) Z₀ 0.10 2.03 13.9 70 0.68 1.61 13.9 1000.89 1.5 13.9 130 1.21 1.09 13.9 160 1.36 0.96 13.9 190

Note that with these example circuit values, a ˜14×tuning ratio for C11is required to fully cover a Z₀ range of about 70Ω to about 190Ω, butonly a 2×tuning ratio for C11 is required to cover a Z₀ range of about100Ω to about 190Ω.

FIG. 6 is a graph showing PAE as a function of power input (Pin) fordifferent values of Z_(INV) (i.e., expressed as “x Ω”) for a modeled TIPcell 302 of the type shown in FIG. 3A, using the values shown inTABLE 1. As can be seen, for particular levels of input power, the PAEcurves can be varied by adjusting the characteristic impedance Z₀(=Z_(INV)) of the TIP cell 302, thereby adjusting α (=R_(L)/Z_(INV)).

Calibration

A TIP circuit 202 may be calibrated to obtain a set of component valuessimilar to those shown in TABLE 1, with the same, more, or fewerdistinct Z₀ settings. One calibration method is to step through thepossible combinations of values for DTCs comprising capacitors C1 andC11, and measure the resulting characteristic impedance Z₀ for thecircuit. If each DTC has 5 control bits, meaning that 2⁵=32 states perDTC can be selected, the number of combinations of values for C1 and C11in a single TIP cell 302 of the type shown in FIG. 3A is 1024 (2⁵×2⁵,assuming that both C1 capacitors are set to the same value for eachcombination). Using multiple TIP cells 302 increases the total number ofavailable combinations.

It may be convenient to select a subset of such DTC combinations thatresult in Z₀ values that closely match desired characteristicimpedances. In any case, the combinations of settings for the DTCs maybe stored in a look-up table that maps DTC state to specific Z₀ values.The look-up table may be implemented as a read-only memory device (e.g.,ROM, PROM, EAROM, EPROM, etc.) which may be used in conjunction withconventional control circuitry.

Methods

Another aspect of the invention includes methods for making a Dohertyamplifier having a tunable impedance and phase circuit that provides anadjustable alpha factor. For example, FIG. 7 is a process flow chartshowing a first method of making a Doherty amplifier, includingproviding a Doherty amplifier having an impedance inverter comprising atunable impedance and phase circuit providing tunability of thecharacteristic impedance of the impedance inverter while maintaining theinsertion phase of a signal through the impedance inverter atapproximately 90° with a selected polarity (e.g., −90° or +90°) (STEP702).

As another example, FIG. 8 is a process flow chart showing a secondmethod of making a Doherty amplifier, including providing the Dohertyamplifier with circuitry for providing a tunable alpha factor (STEP802).

As yet another example, FIG. 9 is a process flow chart showing a thirdmethod of making a Doherty amplifier, including providing a Dohertyamplifier having an impedance inverter comprising at least one digitallytunable circuit configured to provide tunability of (1) thecharacteristic impedance of the Doherty amplifier, and (2) the phase ofa signal input to the impedance inverter to maintain the phase of thesignal at approximately 90° with a selected polarity.

Other embodiments of the above methods may include one or more of thefollowing aspects: wherein the phase of the signal through the impedanceinverter is maintained at 90° ±about 10° with a selected polarity;wherein the phase of the signal through the impedance inverter ismaintained at 90°±about 5° with a selected polarity; wherein the tunableimpedance and phase circuit includes one or more series-connected and/orparallel-connected tunable impedance and phase cells; wherein the atleast one tunable impedance and phase cell utilizes at least onedigitally tunable capacitor to provide tunability; wherein the at leastone tunable impedance and phase circuit comprises one of an LCL circuitor a CLC circuit or an LC circuit or a CL circuit; wherein the tunableimpedance and phase circuit is configured in one of a pi-type ortee-type configuration; wherein the circuitry for providing a tunablealpha factor provides tunability of the characteristic impedance of theDoherty amplifier; wherein the circuitry for providing a tunable alphafactor provides tunability of the phase of a signal input to maintainthe phase of the signal at approximately 90° with a selected polarity;wherein the circuitry for providing a tunable alpha factor includes atleast one tunable circuit comprising one of an LCL circuit or a CLCcircuit or an LC circuit or a CL circuit; wherein the circuitry forproviding a tunable alpha factor includes at least one tunable circuitconfigured in one of a pi-type or tee-type configuration; wherein thephase of the signal is maintained at 90°±about 10° with a selectedpolarity; wherein the phase of the signal is maintained at 90°±about5°with a selected polarity; further including adjusting the tunable alphafactor for different modulations of an input signal; and furtherincluding adjusting the tunable alpha factor for different power levelsof an input signal.

Uses

Circuits and devices in accordance with the present invention may beused alone or in combination with other components, circuits, anddevices. Embodiments of the present invention may be fabricated asintegrated circuits (ICs), which may be encased in IC packages and/or ormodules for ease of handling, manufacture, and/or improved performance.

Circuits in accordance with the present invention are useful in a widevariety of larger radio frequency (RF) circuits for performing a rangeof functions. Such functions are useful in a variety of applications,such as radar systems (including phased array and automotive radarsystems), radio systems, and test equipment. Such circuits may be usefulin systems operating over some or all of the RF range (e.g., from around20 kHz to about 300 GHz).

Radio system usage includes cellular radios systems (including basestations, relay stations, and hand-held transceivers) that use suchtechnology standards as various types of orthogonal frequency-divisionmultiplexing (“ODFM”), various types of quadrature amplitude modulation(“QAM”), Code Division Multiple Access (“CDMA”), Wide Band Code DivisionMultiple Access (“WCDMA”), Global System for Mobile Communications(“GSM”), Enhanced Data Rates for GSM Evolution (EDGE), Long TermEvolution (“LTE”), 5G New Radio (“5G NR”), as well as other radiocommunication standards and protocols.

In particular, the present invention is useful in portablebattery-operated devices, such as cellular telephones, that wouldbenefit from utilizing a Doherty amplifier circuit having a tunableimpedance and phase circuit that provides an adjustable alpha factor.The adjustable alpha factor allows for a selection of PAE curves over awide range of power levels, thereby allowing greater control of currentconsumption in such devices, and thus enabling better battery life.

Fabrication Technologies & Options

The term “MOSFET”, as used in this disclosure, means any field effecttransistor (FET) with an insulated gate and comprising a metal ormetal-like, insulator, and semiconductor structure. The terms “metal” or“metal-like” include at least one electrically conductive material (suchas aluminum, copper, or other metal, or highly doped polysilicon,graphene, or other electrical conductor), “insulator” includes at leastone insulating material (such as silicon oxide or other dielectricmaterial), and “semiconductor” includes at least one semiconductormaterial.

As should be readily apparent to one of ordinary skill in the art,various embodiments of the invention can be implemented to meet a widevariety of specifications. Unless otherwise noted above, selection ofsuitable component values is a matter of design choice and variousembodiments of the invention may be implemented in any suitableintegrated circuit (IC) technology (including but not limited to MOSFETstructures), or in hybrid or discrete circuit forms. Integrated circuitembodiments may be fabricated using any suitable substrates andprocesses, including but not limited to standard bulk silicon,silicon-on-insulator (SOI), and silicon-on-sapphire (SOS). Unlessotherwise noted above, the invention may be implemented in othertransistor technologies such as bipolar, GaAs HBT, GaN HEMT, GaAs pHEMT,and MESFET technologies. However, the inventive concepts described aboveare particularly useful with an SOI-based fabrication process (includingSOS), and with fabrication processes having similar characteristics.Fabrication in CMOS on SOI or SOS processes enables circuits with lowpower consumption, the ability to withstand high power signals duringoperation due to FET stacking, good linearity, and high frequencyoperation (i.e., radio frequencies up to and exceeding 50 GHz).Monolithic IC implementation is particularly useful since parasiticcapacitances generally can be kept low (or at a minimum, kept uniformacross all units, permitting them to be compensated) by careful design.

Voltage levels may be adjusted, or voltage and/or logic signalpolarities reversed, depending on a particular specification and/orimplementing technology (e.g., NMOS, PMOS, or CMOS, and enhancement modeor depletion mode transistor devices). Component voltage, current, andpower handling capabilities may be adapted as needed, for example, byadjusting device sizes, serially “stacking” components (particularlyFETs) to withstand greater voltages, and/or using multiple components inparallel to handle greater currents. Additional circuit components maybe added to enhance the capabilities of the disclosed circuits and/or toprovide additional functionality without significantly altering thefunctionality of the disclosed circuits.

CONCLUSION

A number of embodiments of the invention have been described. It is tobe understood that various modifications may be made without departingfrom the spirit and scope of the invention. For example, some of thesteps described above may be order independent, and thus can beperformed in an order different from that described. Further, some ofthe steps described above may be optional. Various activities describedwith respect to the methods identified above can be executed inrepetitive, serial, or parallel fashion.

It is to be understood that the foregoing description is intended toillustrate and not to limit the scope of the invention, which is definedby the scope of the following claims, and that other embodiments arewithin the scope of the claims. (Note that the parenthetical labels forclaim elements are for ease of referring to such elements, and do not inthemselves indicate a particular required ordering or enumeration ofelements; further, such labels may be reused in dependent claims asreferences to additional elements without being regarded as starting aconflicting labeling sequence).

1. A Doherty amplifier including an impedance inverter comprising alumped-element digitally tunable impedance and phase circuit providingtunability of both an impedance state of the impedance inverter and aphase shift state of the impedance inverter so as to maintain, over arange of impedances, the insertion phase of a signal through theimpedance inverter at approximately 90° with a selected polarity.
 2. Theinvention of claim 1, wherein the phase of the signal through theimpedance inverter is maintained at 90°±about 10° with the selectedpolarity.
 3. The invention of claim 1, wherein the phase of the signalthrough the impedance inverter is maintained at 90°±about 5° with theselected polarity.
 4. The invention of claim 1, wherein thelumped-element digitally tunable impedance and phase circuit includesone or more series-connected and/or two or more parallel-connectedtunable impedance and phase cells.
 5. The invention of claim 4, whereinthe at least one tunable impedance and phase cell utilizes at least onedigitally tunable capacitor to provide tunability.
 6. The invention ofclaim 4, wherein the at least one lumped-element digitally tunableimpedance and phase circuit comprises one of an LCL circuit or a CLCcircuit or an LC circuit or a CL circuit.
 7. The invention of claim 1,wherein the lumped-element digitally tunable impedance and phase circuitis configured in one of a pi-type or tee-type configuration.
 8. Theinvention of claim 1, wherein the lumped-element digitally tunableimpedance and phase circuit provides a tunable alpha factor for theDoherty amplifier.
 9. The invention of claim 1, wherein a plurality ofimpedance states are mapped to a corresponding plurality of phase shiftstates, and the mapped states are stored in a lookup table configured totune both the impedance state of the impedance inverter and the phaseshift state of the impedance inverter so as to maintain, over a range ofimpedances, the insertion phase of a signal through the impedanceinverter at approximately 90° with a selected polarity.
 10. (canceled)11. (canceled)
 12. (canceled)
 13. (canceled)
 14. (canceled)
 15. Theinvention of claim 8, wherein the tunable alpha factor is adjusted fordifferent modulations of an input signal.
 16. The invention of claim 8,wherein the tunable alpha factor is adjusted for different power levelsof an input signal.
 17. A Doherty amplifier including an impedanceinverter including at least one lumped-element digitally tunable circuitconfigured to provide concurrent tunability of both the characteristicimpedance of the impedance inverter and the phase of a signal input tothe impedance inverter so as to maintain, over a range of impedances,the phase of the signal at approximately 90° with a selected polarity.18. The invention of claim 17, wherein the phase of the signal ismaintained at 90°±about 10° with the selected polarity.
 19. Theinvention of claim 17, wherein the phase of the signal is maintained at90°±about 5° with the selected polarity. 20.-38. (canceled)